<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>盒子模型</title>
    <style>
      h1 {
        border: 5px solid red;
        width: 200px;
        height: 100px;
        border-radius: 100px;/*设置圆角 值越大越圆 当值超过宽高的一般为正圆*/
      }
      #d1 {
        width: 100px;
        height: 100px;
        border: 1px solid blue;
        padding-left: 50px;
        padding-top: 50px;
        box-sizing: border-box;/*内边距不影响整体的宽度*/
      }
      #d2 {
        width: 100px;
        height: 100px;
        border: 1px solid green;
      }
    </style>
</head>
<body>
  <h1>这是一个h1</h1>
  <div id="d1">内边距</div>
  <div id="d2">边框</div>
</body>
</html>